Since carbonated water has an excellent heat-retaining effect, it has been used from the old days at a bathhouse utilizing a hot spring or the like. It is considered that the heat retaining effect of the carbonated water is owing to an improvement of a body environment according to a peripheral vasodilator action of a contained carbonic acid gas. Moreover, by a percutaneous introduction of the carbonic acid gas, an increase and an expansion of a capillary bed is brought about so as to improve a blood circulation to the skin. Therefore, it is said to be effective for a retrogressive lesion and a capillary circulation disorder.
Recently, particularly for a treatment mentioned above, it has been revealed that a further remarkable effect can be obtained when a carbonic acid gas concentration in the carbonated water is about 1,200 mg/L, which is a supersaturated concentration range in the water of about 40° C.
As production processes for the carbonated water, there are an one pass supply type for producing the carbonated water by passing hot water obtained from a hot water supplying device or the like in a carbonic acid gas dissolving device only one time, a circulation supply type of circulating hot water in a bath by a circulating pump via a carbonic gas dissolving device, and a dispersion type of directly dispersing a carbonic acid gas in hot water in a bath or the like.
Moreover, as processes for efficiently obtaining high-concentration carbonated water, a process of using a static mixer (see Japanese Patent Application Laid-Open (JP-A) Nos. 63-242258 and 63-242257), and a process of dissolving a carbonic acid gas in hot water via a hollow fiber membrane (see JP-A No. 8-19784) are known.
Although the static mixer is accessible inexpensively and thus it is advantageous, high-concentration carbonated water cannot be produced unless dissolving conditions such as a number of elements and water passage conditions can be controlled. According to the above-mentioned JP-A No. 63-242258, only a static mixer having 12 elements is disclosed without discussion of a kind of the static mixer or the like, and thus carbonated water of the high-concentration cannot be produced efficiently.
Moreover, according to an example of the above-mentioned JP-A No. 63-242257, as long as 30 minutes of time is required for obtaining 1,000 mg/L carbonic acid gas concentration in hot water of 200 L as a standard bath capacity. In order to shorten the time, there is a method of increasing a carbonic acid gas flow rate, however, since a dissolving efficiency is lowered, it is not preferable.
According to the process of using the hollow fiber membrane of the above-mentioned JP-A No. 8-19784, even though carbonated water of a higher concentration can be produced compared with the process of using the static mixer, it tends to be relatively expensive.
An object of the present invention is to provide equipment and a process for producing the carbonated water, capable of producing high-concentration carbonated water easily and efficiently.